Aircraft comprising a cooling system for operation with a two-phase refrigerant

ABSTRACT

An aircraft includes a cooling system having a cooling circuit to circulate a two-phase refrigerant therethrough, an evaporator disposed in a first section of the cooling circuit and having a refrigerant inlet and outlet, a condenser disposed in a second section of the cooling circuit and having a refrigerant inlet and outlet, a first cooling circuit control valve disposed in the cooling circuit between the refrigerant outlet of the evaporator and the refrigerant inlet of the condenser, and a second cooling circuit control valve disposed in the cooling circuit between the refrigerant outlet of the condenser and the refrigerant inlet of the evaporator. The first and the second cooling circuit control valves in their closed state seal the first section of the cooling circuit from the second section of the cooling circuit. The second section of the cooling circuit is installed in an unpressurized region of the aircraft.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is entitled to and claims the benefit of European Application No. 12 172 981.8 filed Jun. 21, 2012 and U.S. Provisional Application No. 61/662,368, filed Jun. 21, 2012, the disclosures of each of which, including the specification, claims, drawings and abstract, are incorporated herein by reference in their entirety.

FIELD

The invention relates to an aircraft comprising a cooling system for operation with a two-phase refrigerant.

BACKGROUND

Cooling systems for operation with a two-phase refrigerant are known from DE 10 2006 005 035 B3, WO 2007/088012 A1, DE 10 2009 011 797 A1 and US 2010/0251737 A1 and may be used to cool various cooling energy consumers present on board an aircraft such as, for example, food that is intended to be supplied to the passengers or heat generating components such as electric or electronic components. In the cooling systems known from DE 10 2006 005 035 B3, WO 2007/088012 A1, DE 10 2009 011 797 A1 and US 2010/0251737 A1 the phase transitions of the refrigerant flowing through the circuit that occur during operation of the system allow the latent heat consumption that then occurs to be utilized for cooling purposes. The refrigerant mass flow needed to provide a desired cooling capacity is therefore markedly lower than for example in a liquid cooling system, in which a one-phase liquid refrigerant is used.

Consequently, the cooling systems described in DE 10 2006 005 035 B3, WO 2007/088012 A1, DE 10 2009 011 797 A1 and US 2010/0251737 A1 may have lower tubing cross sections than a liquid cooling system with a comparable cooling capacity and hence have the advantages of a lower installation volume and a lower weight. What is more, the reduction of the refrigerant mass flow makes it possible to reduce the conveying capacity needed to convey the refrigerant through the cooling circuit of the cooling system. This leads to an increased efficiency of the system because less energy is needed to operate a corresponding conveying device, such as for example a pump, and moreover less additional heat generated by the conveying device during operation of the conveying device has to be removed from the cooling system.

A cooling system for operation with a two-phase refrigerant which is installed in an aircraft usually serves to provide cooling energy to cooling energy consumers arranged in a cabin of the aircraft. The two-phase refrigerant therefore has to be conveyed into and through a region of the aircraft which is occupied with passengers and crew members. Typical two-phase refrigerants for use in aircraft cooling systems such as, for example, CO₂ or R134A (CH₂F—CF₃) evaporate when being subjected to the ambient conditions prevailing in an aircraft cabin during normal operation of the aircraft. A leakage of refrigerant from the cooling system, for example due to a defect or a malfunctioning of the cooling system, and in particular a leakage of the cooling system in the region of the aircraft cabin is undesirable.

SUMMARY

The invention is directed to the object to provide an aircraft equipped with a cooling system for operation with a two-phase refrigerant which allows preventing refrigerant leaking from the cooling system in the pressurized region of the aircraft. This object is achieved by an aircraft having features of attached claims.

In the context of the present application the term “pressurized region” designates an aircraft region which during flight may be pressurized so as to increase the pressure in said aircraft region above the low pressure prevailing outside the aircraft at high altitudes. The pressurized region of the aircraft may comprise a cabin of the aircraft, the cabin including for example a passenger cabin area, a cockpit, a crew rest compartment, a freight compartment, etc. Of course, the aircraft region which herein is designated as a pressurized region of the aircraft during certain operational phases of the aircraft, for example during ground operation or during flight at low altitudes may also be not pressurized. To the contrary, the term “unpressurized region” in the context of the present application designates an aircraft region which also during flight at high altitudes is not pressurized. The pressure prevailing in the pressurized region of the aircraft thus during all operational phases of the aircraft corresponds to the pressure prevailing outside the aircraft. The unpressurized region of the aircraft may, for example, comprise a belly fairing or a tail cone of the aircraft. The term “ambient air” in the context of the present application designates the air in the pressurized region of the aircraft.

An aircraft according to the invention comprises a cooling system which is in particular suitable for cooling heat generating components or food. The cooling system comprises a cooling circuit allowing circulation of a two-phase refrigerant therethrough. The two-phase refrigerant circulating in the cooling circuit is a refrigerant, which upon releasing cooling energy to a cooling energy consumer is converted from the liquid to the gaseous state of aggregation and is then converted back to the liquid state of aggregation. The two-phase refrigerant may for example be R134A (CH₂F—CF₃). Electric or electronic systems, such as avionic systems or fuel cell systems usually have to be cooled at a higher temperature level than food. For cooling these systems, for example Galden® can be used as a two-phase refrigerant.

Preferably, however, CO₂ is employed as the two-phase refrigerant. Although not being non-hazardous to the health of people staying in a cabin of the aircraft in the event of a leakage of the cooling system, CO₂ is at least substantially environment-neutral. If desired, an odorant may be mixed to the refrigerant so that refrigerant leaking from the cooling system due to a defect or a malfunctioning of the cooling system may be smelled by people being subjected to the refrigerant vapor.

An evaporator of the cooling system, which forms an interface between the cooling circuit and a cooling energy consumer, is disposed in a first section of the cooling circuit and has a refrigerant inlet and a refrigerant outlet. The evaporator may, for example, be a heat exchanger which provides for a thermal coupling of the refrigerant flowing through the cooling circuit and a fluid to be cooled, such as for example air to be supplied to mobile transport containers for cooling food stored in the mobile transport containers or any heat generating component on board the aircraft. The two-phase refrigerant is supplied to the refrigerant inlet of the evaporator in its liquid state of aggregation. Upon releasing its cooling energy to the cooling energy consumer, the refrigerant is evaporated and thus exits the evaporator at the refrigerant outlet in its gaseous state of aggregation.

The cooling system further comprises a condenser, which is disposed in a second section of the cooling circuit and has a refrigerant inlet and a refrigerant outlet. The refrigerant which is evaporated in the evaporator, via a portion of the cooling circuit downstream of the evaporator and upstream of the condenser, is supplied to the refrigerant inlet of the condenser in its gaseous state of aggregation. In the condenser, the refrigerant is condensed and hence exits the condenser at the refrigerant outlet of the condenser in its liquid state of aggregation. The condenser may be a part of a chiller or can be supplied with cooling energy from a chiller. For example, the condenser may comprise a heat exchanger which provides for a thermal coupling of the refrigerant flowing through the cooling circuit and a cooling circuit of a chiller.

Refrigerant condensed in the condenser may be immediately directed back to the evaporator. It is, however, also conceivable to provide the cooling system with at least one accumulator which may be disposed in the second section of the cooling circuit downstream of the condenser and thus can be supplied with liquid refrigerant from the condenser. Suitable valves may be provided for controlling the supply of refrigerant from the condenser to the accumulator(s) and/or from the accumulator(s) to the evaporator. Moreover, a super-cooler may be associated with the condenser which serves to super-cool the liquid refrigerant and to thus prevent an undesired evaporation of the refrigerant.

A first cooling circuit control valve is disposed in the cooling circuit between the refrigerant outlet of the evaporator and the refrigerant inlet of the condenser. Further, a second cooling circuit control valve is disposed in the cooling circuit between the refrigerant outlet of the condenser and the refrigerant inlet of the evaporator. In their closed state, the first and the second cooling circuit control valve are adapted to seal the first section of the cooling circuit from the second section of the cooling circuit. The second section of the cooling circuit together with the cooling system components disposed in the second section of the cooling circuit is installed in an unpressurized region of the aircraft. For example, the second section of the cooling circuit may be in installed in the tail cone or the belly fairing of the aircraft.

The first section of the cooling circuit may also be installed in an unpressurized region of the aircraft. In practice, it is, however, preferable to install the first section of the cooling circuit or at least some of the cooling system components disposed in the first section of the cooling circuit in a pressurized region, i.e. a cabin of the aircraft. For example, at least the evaporator of the cooling system may be installed in the aircraft cabin when said evaporator serves to provide cooling energy to a cooling energy consumer which is also installed in the aircraft cabin.

In the event of a leakage occurring in the cooling system, by closing the first and the second cooling circuit control valve, the first and the second section of the cooling circuit can be sealed from each other. Hence, the maximum amount of refrigerant exiting the cooling system in the event of a leakage of the cooling system is reduced to the amount of refrigerant contained in the section of the cooling circuit which is affected by the leakage, i.e. either the first or the second section of the cooling circuit. If desired, the cooling system may comprise more than two valves which are adapted to seal selected areas of the cooling circuit from each other so as to further reduce the maximum amount of refrigerant exiting the cooling system in the event of a leakage of the cooling system.

Further, the installation of the second section of the cooling circuit including the cooling system components disposed in said second cooling circuit section in an unpressurized region of the aircraft enables refrigerant exiting from the cooling system due to a leakage of the second section of the cooling circuit to be vented to the environment without harming people staying in the aircraft cabin, i.e. a pressurized region of the aircraft. In particular cooling system components containing a large amount of refrigerant, such as accumulators, storage containers and the like, preferably should be disposed in the second section of the cooling circuit and thus installed in an unpressurized region of the aircraft so as to allow the refrigerant to be vented to the environment in the event of a leakage of the second section of the cooling circuit. The aircraft according to the invention thus allows to considerably minimize the health risk for people staying in the aircraft cabin due to a contamination of the ambient air in the aircraft cabin with refrigerant leaking from the cooling system, for example due to a defect or a malfunctioning of the cooling system.

The cooling system employed in the aircraft according to the invention may further comprise a first bleed valve arrangement which in its open state is adapted to discharge refrigerant from the first section of the cooling circuit to the aircraft environment and/or to an unpressurized region of the aircraft. Alternatively or additionally thereto, the cooling system may comprise a second bleed valve arrangement which in its open state is adapted to discharge refrigerant from the second section of the cooling circuit to the aircraft environment and/or to an unpressurized region of the aircraft.

By venting refrigerant from the cooling circuit of the cooling system to the aircraft environment and/or to an unpressurized region of the aircraft, the amount of refrigerant which in the event of a defect or a malfunctioning of the cooling system may enter the aircraft cabin and harm people staying in the aircraft cabin can further be minimized. Further, by discharging refrigerant from the cooling system to the aircraft environment and/or to an unpressurized region of the aircraft, an uncontrolled pressure increase in the cooling system or selected cooling system components may be prevented which may otherwise result from liquid refrigerant being enclosed in the first or the second section of the cooling circuit as a result of the closing of the first and the second cooling circuit control valve.

The cooling system may further comprise a control device which is configured to control the first and/or the second cooling circuit control valve, the first bleed valve arrangement and/or the second bleed valve arrangement in dependence on at least one sensor signal supplied to the control device. The sensor signal may for example be indicative of a pressure of the refrigerant in the cooling circuit of the cooling system. For example, a sudden pressure drop occurring during normal operation of the cooling system, by the control device, may be interpreted as indicative of a leakage of the cooling system and, hence, cause the control device to close the first and the second cooling circuit control valve so as to seal the first and the second section of the cooling system cooling circuit from each other. To the contrary, when the first and the second cooling circuit control valve are closed, a pressure increase in the first and/or the second section of the cooling circuit above a predetermined threshold value may trigger the control device to control the first bleed valve arrangement and/or the second bleed valve arrangement in its/their open state so as to discharge refrigerant from the first and/or the second section of the cooling circuit.

Alternatively or additionally thereto, the control device may be adapted to evaluate a sensor signal indicative of a concentration of the refrigerant in the ambient air in a pressurized region of the aircraft. For example, at least one sensor for measuring the concentration of the refrigerant in the ambient air may be installed in the aircraft cabin. This sensor may be associated exclusively to the cooling system, but also may form a part of the air quality monitoring system of an aircraft air conditioning system. In case CO₂ is employed in the cooling system as the two-phase refrigerant, a sensor for measuring the CO₂ concentration in the ambient air in the aircraft cabin, due to the specific weight of CO₂ being higher than the specific weight of air, preferably is placed close to the floor of the aircraft cabin.

In case a concentration of the refrigerant in the ambient air in the pressurized region of the aircraft exceeds a predetermined threshold value, the control device may close the first and the second cooling circuit control valve so as to seal the first and the second section of the cooling system cooling circuit from each other. Further, the control device may control the first and/or the second bleed valve arrangement so as to allow refrigerant to be vented from the cooling system. Additionally or alternatively thereto, the control device may also be adapted to output a visually or acoustically recognizable warning signal. Further, the control device may be adapted to control an actuating mechanism of an oxygen mask system of the aircraft. The actuating mechanism may cause oxygen masks to drop from a ceiling of the aircraft cabin so as to become accessible to the passengers and the crew members staying in the aircraft cabin, if the refrigerant concentration in the breathing air in the aircraft cabin exceeds a predetermined threshold value.

The control device may further be adapted to evaluate a sensor signal or a plurality of sensor signals indicative of an amount of refrigerant present in the cooling circuit of the cooling system. For example, the amount of refrigerant present in the cooling circuit of the cooling system may be determined by measuring the level of the refrigerant in an accumulator, the pressure of the refrigerant, and the temperature of the refrigerant. The amount of refrigerant present in the cooling circuit of the cooling system may be determined continuously or at specific time intervals. If desired, a first measurement upon start-up of the system may be used as a reference measurement and compared at least to a measurement performed during or after system shut-down.

A considerable decrease of the amount of refrigerant in the cooling circuit of the cooling system during operation of the cooling system may be indicative of a leakage of the cooling system. In case the refrigerant loss is low, the control device may simply initiate shut-down of the operation of the cooling system. In the event of a refrigerant leakage which may cause harm to people on board the aircraft, the control device, however, may also control the first and the second cooling circuit control valve so as to seal the first and the second section of the cooling system cooling circuit from each other and/or to discharge refrigerant from the cooling system to the aircraft environment and/or to an unpressurized region of the aircraft by means of the first and/or the second bleed valve arrangement.

Moreover, the control device may be adapted to evaluate at least one sensor signal indicative of a system failure affecting proper operation of the cooling system. For example, the control device may be adapted to close the first and the second cooling circuit control valve so as to seal the first and the second section of the cooling system cooling circuit from each other and/or control the first and/or the second bleed valve arrangement so as to discharge refrigerant from the cooling system cooling circuit to the aircraft environment and/or to an unpressurized region of the aircraft in the event of a power failure or a malfunctioning of the condenser.

Finally, the control device may be adapted to evaluate at least one sensor signal indicative of a predefined operating state of the aircraft. The predefined operating state of the aircraft may be an emergency operating state, for example prior to an intended emergency landing or in case of a fire on board the aircraft. For example, the control device may be adapted to close the first and the second cooling circuit control valve so as to seal the first and the second section of the cooling system cooling circuit from each other and/or control the first and/or the second bleed valve arrangement so as to discharge refrigerant from the cooling system cooling circuit to the aircraft environment and/or to an unpressurized region of the aircraft when an emergency operating state of the aircraft is detected.

At least one component of the cooling system which is installed in a pressurized region of the aircraft may comprise an encasement. The encasement may be adapted to receive refrigerant leaking from the at least one component of the cooling system. The at least one component of the cooling system may, for example, be a tubing, in particular a tubing forming a component of the first section of the cooling circuit or the evaporator. The encasement may be sealed against the environment so as to avoid refrigerant leaking from the encased component to contaminate the ambient air in the pressurized region of the aircraft. Preferably, the encasement is connectible to the aircraft environment and/or an unpressurized region of the aircraft so as to be able to vent refrigerant from the encasement to the aircraft environment and/or the unpressurized region of the aircraft. At least one sensor for measuring the pressure and/or the concentration of the refrigerant in the encasement may be provided. The signals of the at least one sensor may be evaluated by the control unit for controlling the first and/or the second cooling circuit control valve, the first bleed valve arrangement and/or the second bleed valve arrangement.

The installation of cooling system components in an encasement preventing refrigerant leaking from the cooling system components to enter a pressurized region of the aircraft allows to significantly reduce the risk that people staying in a pressurized region of the aircraft are harmed by a refrigerant contamination of the breathing air in the pressurized region of the aircraft. Further, in particular when at least one sensor for measuring the pressure and/or the refrigerant concentration in the encasement is present, localization of a leakage of the cooling system is simplified. Encasements, however, undesirably add to the weight of the cooling to system.

A control device of the cooling system preferably is configured to control the operation of the cooling system upon system start-up such that refrigerant is liquefied in the condenser while the first cooling circuit control valve and the second cooling circuit control valve are closed so as to separate the first section of the cooling circuit from the second section of the cooling circuit. In other words, the condenser is operated so as to liquefy refrigerant while the refrigerant still is not conveyed to the evaporator. The liquefaction of the refrigerant in the condenser is continued until the amount of liquid refrigerant is sufficient to allow a flooding of cooling system components which are disposed in the cooling circuit downstream of a conveying device for conveying refrigerant through the cooling circuit with liquid refrigerant. The liquid refrigerant may be stored in an accumulator.

Advantageously, the control device is configured to operate the condenser during the start-up operational phase of the cooling system at a low operating temperature, i.e. an operating temperature that is lower than the operating temperature of the condenser during normal operation of the cooling system, so as to allow super-cooling of the liquid refrigerant. Alternatively or additionally thereto, a separate super-cooler or a super-cooler which is integrated into the condenser may be employed so as to ensure the desired super-cooling of the refrigerant during the start-up operational phase of the cooling system.

An operating state of the cooling system wherein the condenser is operated so as liquefy refrigerant, although the amount of liquid refrigerant present in the cooling circuit is already sufficient to allow the desired flooding of cooling system components, while the supply of refrigerant to the evaporator, however, still is interrupted, in the following is designated as a stand-by operational state of the cooling system. When the cooling system is in the stand-by operational state, the desired flooding of the cooling system components with liquid refrigerant and the supply of liquid refrigerant to the evaporator may be initiated so as to allow start of normal operation of the cooling system wherein the cooling system provides cooling energy to at least one cooling energy consumer. It is, however, also possible to simply cease operation of the condenser of a cooling system operating in the stand-by operational state so as to shut-down the cooling system.

Preferably, a control device of the cooling system is configured to control the operation of the cooling system in such a way that the cooling system is operated in its stand-by operational state as long as possible. Operation of the cooling system in the stand-by operational state allows to immediately recognize operational failures and, in particular, leakages of the system which may not be noticed when the system is shut off. The operational safety of the cooling system operated in its stand-by operational state, however, still is particularly high, since the supply of refrigerant to the first section of the cooling circuit and thus into a pressurized region of the aircraft still is interrupted.

System start-up until the stand-by operational state of the cooling system is reached therefore may be initiated by the control device, although there are still no cooling energy requirements from cooling energy consumers supplied with cooling energy by the cooling system during normal operation of the cooling system. For example, initiating the start-up procedure of the cooling system may be made subject of a checklist which is processed during a flight preparation operational phase of the aircraft. The stand-by operation of the cooling system may be terminated and normal operation of the cooling system including operation of the evaporator may be started as soon as cooling energy has to be supplied to the cooling energy consumers provided with cooling energy by the cooling system.

A control device of the cooling system may further be configured to control the supply of refrigerant to the evaporator during normal operation of the cooling system in dependence on the operational state of the evaporator, i.e. the cooling energy requirement of the cooling energy consumer coupled to the evaporator, such that a dry evaporation of the refrigerant occurs in the evaporator. This allows an operation of the cooling system with a limited amount of refrigerant circulating in the cooling circuit. As a result, the static pressure of the refrigerant prevailing in the cooling circuit in the non-operating state of the cooling system is low, even at high ambient temperatures. In addition, the health risk for people staying in the aircraft cabin due to a contamination of the ambient air in the aircraft cabin with refrigerant leaking from the cooling system is further reduced.

The supply of refrigerant to the evaporator may be is controlled by suitably controlling a respective valve which is disposed in the cooling circuit upstream of the evaporator. The valve may comprise a nozzle for spraying the refrigerant into the evaporator and to distribute the refrigerant within the evaporator. The spraying of the refrigerant into the evaporator may be achieved, for example, by supplying refrigerant vapor from the evaporator to the nozzle of the valve and/or by evaporation of the refrigerant due to a pressure decrease of the refrigerant downstream of the valve.

To ensure occurrence of a dry evaporation in the evaporator, a predetermined amount of refrigerant may be supplied to the evaporator by appropriately controlling the valve. Then, a temperature TK1 of the refrigerant at the refrigerant inlet of the evaporator and a temperature TA2 of the fluid to be cooled by the evaporator, for example air supplied to the cooling energy consumer, may be measured, preferably while a fan conveying the fluid to be cooled to the cooling energy consumer is running. Further, the pressure of the refrigerant in the evaporator or at the refrigerant outlet of the evaporator may be measured. If a temperature difference between the temperature TA2 of the fluid to be cooled by the evaporator and the temperature TK1 of the refrigerant at the refrigerant inlet of the evaporator exceeds a predetermined threshold value, for example 8K, and the pressure of the refrigerant in the evaporator lies within a predetermined range, the refrigerant supplied to the evaporator is thoroughly evaporated and possibly also super-heated by the evaporator. Hence, the valve again may be controlled so as to supply a further predetermined amount of refrigerant to the evaporator.

A control device of the cooling system further may be configured to control the operation of the cooling system upon system shut-down such that the supply of refrigerant to the evaporator is interrupted, while liquefaction of refrigerant in the condenser is continued. During this operational phase of the cooling system the first and the second cooling circuit control valve, however, are still open such that the first and the second section of the cooling circuit are still connected to each other. The continued liquefaction of the refrigerant present in the cooling system results in a pressure decrease in the cooling circuit, and thus in an evaporation of residual liquid which may be present, in particular, in the first section of the cooling circuit. An evaporation of residual liquid present in the first section of the cooling circuit and the removal of this refrigerant from the first section of the cooling circuit allows to prevent that this refrigerant evaporates when the cooling system is shut off, for example due to high ambient temperatures, and causes the built-up of an undesirable high pressure in the first section of the cooling circuit.

Preferably, the control device is configured to operate the condenser at a low operating temperature, i.e. an operating temperature which is lower than the operating temperature of the condenser during normal operation of the cooling system. A low operating temperature of the condenser increases the pressure drop occurring in the cooling system during the shut-down procedure and, as a result, supports the evaporation of residual liquid present in cooling circuit.

The operating temperature of the condenser and thus the amount of refrigerant which may be liquefied in the condenser, however, is limited by the design of the condenser and the thermodynamic properties of the refrigerant. Further, the pressure of the refrigerant in the cooling system or at specific locations in the cooling system may be measured with a higher accuracy than the temperature of the refrigerant in the cooling system or at specific locations in the cooling system. Therefore, the control device is configured to use the pressure of the refrigerant in the cooling system or at specific locations in the cooling system as a control parameter for controlling the operation of the cooling system, in particular the operation of the condenser and the operation of control valves which control the flow of refrigerant through the cooling circuit. Specifically, the control device may be configured to continue the shut-down procedure involving an interruption of the supply of refrigerant to the evaporator and a continued liquefaction of refrigerant in the condenser until a pressure of the refrigerant in the cooling system which may be measured at different locations in the cooling system or at a specific location in the cooling system has reached a predetermined set value.

The predetermined set value of the pressure of the refrigerant in the cooling system preferably is lower than a value of the pressure of the refrigerant in the cooling system during normal operation of the cooling system. By continuing the shut-down procedure until the pressure of the refrigerant in the cooling system is lower than during normal operation of the cooling system, the desired evaporation of residual liquid refrigerant as described above is ensured.

A control device of the cooling system preferably further is configured to close the first and the second cooling circuit control valves so as to separate the first section of the cooling circuit from the second section of the cooling circuit when the pressure of the refrigerant in the cooling system has reached the predetermine set value. In this operational state of the cooling system, an essential amount of refrigerant present in the cooling system is liquefied, i.e. only a small amount of refrigerant remains in the first section of the cooling circuit. Hence, in the event of a leakage of the cooling system in the region of the first section of the cooling circuit, only a small amount of refrigerant will enter the pressurized region of the aircraft. When the first and the second cooling circuit control valve are closed, operation of the cooling system in its standby operational state may be continued, i.e. liquefaction of the refrigerant in the condenser may be continued, although the first and the second section of the cooling circuit are sealed from each other. It is, however, also possible to completely shut off the cooling system, i.e. to also cease the operation of the condenser.

A control device of the cooling system preferably is configured to control the operation of the cooling system upon system shut-down such that refrigerant which is liquefied in the condenser is stored in an accumulator which is installed in an unpressurized region of the aircraft. As a result, after complete shut off of the cooling system, the major part of the refrigerant present in the cooling system is stored outside of the pressurized region of the aircraft, i.e. the aircraft cabin. This ensures that in the event of a leakage, the major part of refrigerant present in the cooling system may be discharged to the unpressurized region of the aircraft and finally the aircraft environment without harming people staying in the pressurized region of the aircraft.

The control functions performed during operation of the cooling system as described above may be carried out be a single control unit, for example a central control unit of the cooling system. It is, however, also conceivable to equip the cooling system with a plurality of control units, each of which carries out only selected control tasks.

A pipe burst safety valve may be associated with each one of the first and the second cooling circuit control valve. A pipe burst safety valve associated with the first cooling circuit control valve may be arranged in the cooling circuit upstream of the first cooling circuit control valve. A pipe burst safety valve associated with the second cooling circuit control valve may be arranged in the cooling circuit downstream of the second cooling circuit control valve. In case a pipe bust should occur in the tubing of the cooling circuit, in particular in the tubing of the first section of the cooling circuit, the pipe burst safety valves immediately close such that the amount of refrigerant exiting the cooling system due to the pipe burst is limited.

The cooling circuit of the cooling system may comprise at least two first sections which are formed separate from each other and which may be sealed from each other. Preferably, the two first sections are at least partially installed in a pressurized region of the aircraft. An evaporator may be disposed in each of the two first cooling circuit sections. For example, at least the evaporators may be installed in a pressurized region of the aircraft. The evaporators disposed in the two first cooling circuit sections may be operated independently from each other, i.e. it is possible to operate an evaporator disposed in one first cooling circuit section, but not to operate an evaporator disposed in the other first cooling circuit section. This allows a particularly energy efficient operation of the cooling system in case only selected cooling energy consumers associated with selected evaporators require the supply of cooling energy. Further, the system operational reliability of a cooling system comprising two first cooling circuit sections is improved, since in case of an operational failure caused by a lack of refrigerant in the cooling circuit, for example due to a leakage of the cooling system, it may still be possible to operate at least one of two first cooling circuit sections. It is, of course, also conceivable to provide the cooling system with more than two first cooling circuit sections.

A control device of the cooling system may be configured to control the two first cooling circuit control valves and/or the two second cooling circuit control valves in such a manner that only one of the two first sections of the cooling circuit is connected to the second section of the cooling circuit if the amount of refrigerant circulating in the cooling circuit is not sufficient to satisfy the demand of both first cooling circuit sections. Such a control of the cooling system prevents that a lack of refrigerant circulating in the cooling circuit, i.e. a lack of cooling energy produced by the cooling system, leads to a sudden failure of the entire system. Instead, the cooling energy produced by the cooling system is directed to a selected one of the two first cooling circuit sections so as to at least supply of cooling energy to said selected one of the two first cooling circuit sections.

Two first cooling circuit control valves as well as two second cooling circuit control valves may be provided and, in their closed state, may be adapted to seal the two first section of the cooling circuit from the second section of the cooling circuit, preferably independently from each other. This allows to further reduce the amount of refrigerant exiting the cooling system and entering a pressurized aircraft region in the event of a leakage of the cooling system. In addition, localization of a cooling system leakage may be simplified by the possibility to independently seal two first cooling circuit sections from the second cooling circuit section.

The cooling system may further comprise a first additional cooling circuit control valve connected in series with the first cooling circuit control valve. Alternatively or additionally thereto, the cooling system may further comprise a second additional cooling circuit control valve connected in series with the second cooling circuit control valve. Two cooling circuit control valves connected in series improve system redundancy in case of a failure of one of the cooling circuit control valves. In a cooling system comprising two first cooling circuit sections, cooling circuit control valves connected in series may be employed to seal either both or only one of the two first cooling circuit sections from the second cooling circuit section.

At least one cooling system component which is susceptible to pipe burst, for example the evaporator, may be disposed between a respective pair of additional pipe burst valves so as to increase the operational safety of the cooling system 10.

The cooling system may further comprises a bypass line bypassing the evaporator. A pressure relief valve and/or a control valve may be adapted to control the refrigerant flow through the bypass line.

BRIEF DESCRIPTION OF DRAWINGS

Preferred embodiments of the invention now are described in more detail with reference to the enclosed schematic drawings, wherein

FIG. 1 depicts an overview over a first embodiment of an aircraft cooling system suitable for operation with a two-phase refrigerant,

FIG. 2 depicts an overview over a second embodiment of an aircraft cooling system suitable for operation with a two-phase refrigerant,

FIG. 3 depicts an overview over a third embodiment of an aircraft cooling system suitable for operation with a two-phase refrigerant,

FIG. 4 depicts an overview over a fourth embodiment of an aircraft cooling system suitable for operation with a two-phase refrigerant,

FIG. 5 depicts an overview over a fifth embodiment of an aircraft cooling system suitable for operation with a two-phase refrigerant, and

FIG. 6 depicts an alternative cooling circuit control valve arrangement which may be employed in the cooling system of FIG. 5.

DETAILED DESCRIPTION

FIG. 1 depicts a cooling system 10 which on board an aircraft, for example, may be employed to cool food provided for supplying to the passengers. The cooling system 10 comprises a cooling circuit 12 allowing circulation of a two-phase refrigerant therethrough. The two-phase refrigerant may for example be CO₂ or R134A. Four evaporators 14 a, 14 b, 14 c, 14 d are disposed in the cooling circuit 12. Each evaporator 14 a, 14 b, 14 c, 14 d comprises a refrigerant inlet 16 a, 16 b, 16 c, 16 d and a refrigerant outlet 18 a, 18 b, 18 c, 18 d. The refrigerant flowing through the cooling circuit 12 is supplied to the refrigerant inlets 16 a, 16 b, 16 c, 16 d of the evaporators 14 a, 14 b, 14 c, 14 d in its liquid state of aggregation. Upon flowing through the evaporators 14 a, 14 b, 14 c, 14 d the refrigerant releases its cooling energy to a cooling energy consumer which in the embodiment of a cooling system 10 depicted in FIG. 1 is formed by the food to be cooled. Upon releasing its cooling energy, the refrigerant is evaporated and hence exits the evaporators 14 a, 14 b, 14 c, 14 d at the refrigerant outlets 18 a, 18 b, 18 c, 18 d of the evaporators 14 a, 14 b, 14 c, 14 d in its gaseous state of aggregation. The supply of refrigerant to the evaporators 14 a, 14 b, 14 c, 14 d is controlled by respective valves 20 a, 20 b, 20 c, 20 d which are disposed in the cooling circuit 12 upstream of the evaporators 14 a, 14 b, 14 c, 14 d, respectively.

Further, the cooling system 10 comprises a first and a second condenser 22 a, 22 b. Each condenser 22 a, 22 b has two refrigerant inlets 24 a, 24 a, 24 b, 24 b′ and a refrigerant outlet 26 a, 26 b. The refrigerant which is evaporated in the evaporators 14 a, 14 b, 14 c, 14 d, via a portion of the cooling circuit 12 downstream of the evaporators 14 a, 14 b, 14 c, 14 d and upstream of the condensers 22 a, 22 b, is supplied to the refrigerant inlets 24 a, 24 a′, 24 b, 24 b′ of the condensers 22 a, 22 b in its gaseous state of aggregation. The condensers 22 a, 22 b are thermally coupled to a chiller (not shown in FIG. 1). The cooling energy provided by the chiller in the condensers 22 a, 22 b is used to condense the refrigerant. Thus, the refrigerant exits the condensers 22 a, 22 b at the refrigerant outlets 26 a, 26 b of the condensers 22 a, 22 b in its liquid state of aggregation.

The condensers 22 a, 22 b may be tube bundle heat exchangers. Tube bundle heat exchangers are robust and may be provided with a receiving space for buffering liquefied refrigerant when the condensers 22 a, 22 b during operation of the cooling system 10 are at least partially flooded to super-cool the liquefied refrigerant. It is, however, also conceivable to design the condensers 22 a, 22 b as plate heat exchangers, in particular if a separate super-cooler for super-cooling the liquefied refrigerant is associated with at least one of the condensers 22 a, 22 b.

Refrigerant circulating in the cooling circuit 12 may be directly supplied to each one of the condensers 22 a, 22 b. The condensers 22 a, 22 b, however, are connected in series such that refrigerant exiting the condenser 22 a is directed through the condenser 22 b so as to ensure sufficient super-cooling of the refrigerant. An accumulator 28 is connected to a refrigerant inlet 24 a′, 24 b′ of each one of the condensers 22 a, 22 b, wherein the supply of refrigerant from the accumulator 28 to the condensers 22 a, 22 b is controlled by means of a valve 30. Further, the refrigerant outlets 26 a, 26 b of the condensers 22 a, 22 b are connected to the accumulator 28 allowing refrigerant liquefied in the condensers 22 a, 22 b to be supplied into the accumulator. The supply of refrigerant from the condensers 22 a, 22 b to the accumulator 28 is controlled by means of a valve 32.

The accumulator 28 comprises an adaptor connector 33 having a pressure regulating function via which refrigerant may be introduced into the cooling system 10 or discharged from the cooling system 10, for example during maintenance of the cooling system 10. A conveying device 34, which is embodied in the form of a pump, serves to convey the refrigerant through the cooling circuit. If desired, an air vessel (not shown in FIG. 1) may be provided in the cooling circuit 12 downstream of the conveying device 34 so as to dampen pressure surges resulting from the operation of the conveying device 34 or the cooling system valves. Specifically, the air vessel may be arranged in the cooling circuit 12 in a manner that it is not possible to flood the air vessel with liquid refrigerant so as to ensure that the air vessel contains a sufficient amount of gas during all operational phases of the cooling system 10.

The accumulator 33 is installed above the condensers 22 a, 22 b and the conveying device 34 is installed below the condensers 22 a, 22 b. Hence, the conveying device 34 is arranged relative to the accumulator 33 and the condensers 22 a, 22 b in such a position that for the conveying device 34 a positive minimum inflow level, which is defined by the level of a liquid column above an inflow edge of a blade of the conveying device 34, is maintained. The gravity of the liquid column causes a defined pressure increase in the refrigerant supplied to the conveying device 34 thus providing for a super-cooling of the refrigerant and thereby preventing evaporation of the refrigerant due to the pressure reduction caused by the conveying device 34. Consequently, cavitation of the conveying device 34 is avoided.

A first cooling circuit control valve 36 is disposed in the cooling circuit 12 downstream of the evaporators 14 a, 14 b, 14 c, 14 d and upstream of the condensers 22 a, 22 b. A second cooling circuit control valve 38 is disposed in the cooling circuit 12 upstream of the evaporators 14 a, 14 b, 14 c, 14 d and downstream of the condensers 22 a, 22 b. In their closed state, the first and the second cooling circuit control valves 36, 38 seal a first section 12 a of the cooling circuit 12 from a second section 12 b of the cooling circuit 12 b. The dash-dotted line in FIG. 1 indicates the boundary between the first and the second section 12 a, 12 b of the cooling circuit 12. The second section 12 b of the cooling circuit 12, together with the cooling system components disposed in the second section 12 b of the cooling circuit 12, is installed in an unpressurized region 40 of the aircraft. For example, the second section 12 b of the cooling circuit 12 may be in installed in the tail cone or the belly fairing of the aircraft. The unpressurized region 40 of the aircraft is connected to the aircraft environment, for example by louvers or suitable vent openings.

The first section 12 a of the cooling circuit 12 is at least partially installed in a pressurized region, i.e. a cabin 42 of the aircraft. In particular, the evaporators 14 a, 14 b, 14 c, 14 d, tubing portions employed in the cooling circuit 12 and the valves 20 a, 20 b, 20 c, 20 d are installed in the aircraft cabin 42.

The cooling system 10 further comprises a first pressure relief valve 44 which, via a connecting line 48 is connected to the cooling circuit 12 downstream of the first cooling circuit control valve 36 and a second pressure relief valve 46 which is connected to the accumulator 38. The first pressure relief valve 44 thus is associated with the first section 12 a of the cooling circuit 12, while the second pressure relief valve 46 is associated with the second section 12 b of the cooling circuit 12. Both pressure relief valves 44, 46 are designed as mechanically actuatable valves which automatically open in case a pressure difference acting on the valves 44, 46 exceeds a threshold value which is determined by the design of the valves 44, 46. It is, however, also conceivable to design the pressure relief valves 44, 46 in the form of burst discs or bust discs may be provided in addition to the pressure relief valves 44, 46.

The pressure relief valves 44, 46 thus prevent a pressure in the cooling system 10 to exceed a desired threshold value independent of the operational state of the cooling system 10. It should be noted that the first pressure relief valve 44, although being associated with the first section 12 a of the cooling circuit 12 is installed in the unpressurized region 40 of the aircraft. Thus, in the event of an undesired pressure increase in the first section 12 a of the cooling circuit 12, the refrigerant present in the first section 12 a of the cooling circuit 12, via the first pressure relief valve 44, is discharged into the unpressurized region 40 of the aircraft, where it does not harm people staying in the aircraft cabin 42. Further, the first pressure relief valve 44 acts as a safety valve for the conveying device 34, for example in case of a control failure resulting in an undesired increase of the pressure in the conveying device 34. The first pressure relief valve 44 thus aids to prevent a leakage and/or damage of the conveying device 34.

In the cooling system 10 of FIG. 1 the arrangement of the second pressure relief valve 46 close to the accumulator 38 is advantageous, since the accumulator 38 forms an interface between a plurality of cooling system components. Further, the volume of the accumulator 38 allows to dampen pressure variations occurring in the cooling circuit 12. It is, however, also conceivable to install the second pressure relief valve 46 in the aircraft outer skin such that refrigerant discharged from the cooling system 10 via the second pressure relief valve 46 is vented directly to the aircraft environment. A second pressure relief valve 46 installed in the aircraft outer skin may be closed by means of a plug arranged flush with the aircraft outer skin. Absence of the plug then immediately indicates that the second pressure relief valve 46 has been opened.

The cooling system 10 further is provided with a bleed valve arrangement 50 which in its open state serves to discharge refrigerant from the second section 12 b of the cooling circuit 12 to the unpressurized region 40 of the aircraft. In the cooling system 10 of FIG. 1 the bleed valve arrangement 50 is formed by an electrically actuatable safety valve which is connected to the accumulator 28. Operation of the cooling system 10 is controlled by means of an electronic control unit 52. In particular, the electronic control unit 52 controls operation of the evaporators 14 a, 14 b, 14 c, 14 d, the condensers 22 a, 22 b and the various valves employed in the cooling circuit.

As becomes apparent from FIG. 1, the evaporator 14 d is received within an encasement 54 which is adapted to receive refrigerant leaking from the evaporator 14 d. The encasement 54 is sealed against the environment so as to avoid refrigerant leaking from the evaporator 14 d to contaminate the ambient air in the cabin 42 of the aircraft. The encasement 54, however, via a line 56 is connected to the unpressurized region 40 of the aircraft. A control valve 58 is disposed in the line 56 and serves to either open the interior of the encasement 54 to the unpressurized region 40 of the aircraft or to seal the interior of the encasement 54 from the unpressurized region 40 of the aircraft.

In the following, operation of the cooling system 10 will be described. Upon system start-up, the control unit 52 controls the operation of the cooling system 10 such that refrigerant is liquefied in the condensers 22 a, 22 b, while the first cooling circuit control valve 36 and the second cooling circuit control valve 38 are closed so as to separate the first section 12 a of the cooling circuit 12 from the second section 12 b of the cooling circuit 12. Further, under the control of the control unit 52, the valves 20 a,20 b, 20 c, 20 d and 30 are closed, while valve 32 is open. The condensers 22 a, 22 b are operated until the condensers 22 a, 22 b are at least partially flooded resulting in a super-cooling of the refrigerant. Specifically, the condensers 22 a, 22 b are operated at a low operating temperature, i.e. an operating temperature that is lower than the operating temperature of the condensers 22 a, 22 b during normal operation of the cooling system so as to support super-cooling of the refrigerant. Due to the conveying device 34 being arranged below the condensers 22 a, 22 b the flooding of the condensers 22 a, 22 b entails that also the conveying device 34 is flooded. Further, since the conveying device 34 is flooded before operation of the conveying device 34 is started, it is not necessary that the conveying device 34 is designed in the form of a self-sucking pump.

When the level of the liquid refrigerant in the conveying device 34 has reached a level which ensures that dry operation of the conveying device 34 is avoided, operation of the conveying device 34 is started. In particular, the operation of the conveying device 34 is started in dependence on a signal indicative of the level of the liquid refrigerant being supplied to the control unit 52. The level of liquid refrigerant may be measured in the condensers 22 a, 22 b, in the conveying device 34 or downstream of the conveying device 34. Any suitable procedure for measuring the level of the liquid refrigerant may be employed. For example, the level of the liquid refrigerant may be measured using a float gauge or by detecting a physical parameter such as the electrical connectivity or the heat conductivity of the refrigerant. Further, inductive, piezoelectric or ultrasonic measurements may be performed. Finally, it is also conceivable to determine the volume of refrigerant which is already liquefied by means of the condensers 22 a, 22 b based on a measurement of the pressure difference in the cooling system 10 and the development of the system pressure after starting operation of the condensers 22 a, 22 b.

When operation of the conveying device 34 is started, the conveying device 34 is operated with a low speed. If desired, the conveying device 34 may be adapted to be operated with a continuously varying speed. It might, however, also be sufficient to set three fixed speeds at which the conveying device 34 may be operated. In this case, the conveying device 34 during a start-up of the cooling system 10 is operated at the lowest speed.

The conveying device 34 conveys refrigerant liquefied in the condensers 22 a, 22 b into the accumulator 28. This operation is continued until the amount of liquid refrigerant present in the cooling circuit 12 and stored in the accumulator 28 is sufficient to allow that cooling system components which are disposed downstream of the conveying device 34, i.e. the tubing of the cooling circuit 12 and the evaporators 14 a, 14 b, 14 c, 14 d can be flooded with liquid refrigerant. The fill level of the liquid refrigerant in the accumulator 28 is measured so as to determine whether enough liquid refrigerant is present to allow the desired flooding of the cooling system components. Further, based on these fill level measurements and based on measurements of the pressure and the temperature of the refrigerant in the cooling system 10, the total amount of refrigerant in the cooling system 10 may be determined.

An operating state of the cooling system 10 wherein the condensers 22 a, 22 b are operated so as liquefy refrigerant, although the amount of liquid refrigerant present in the cooling circuit 12 is already sufficient to allow the desired flooding of cooling system components, while the supply of refrigerant to the evaporators 14 a, 14 b, 14 c, 14 d, however, still is interrupted is designated as a stand-by operational state of the cooling system 10. The control device 52 of the cooling system 10 controls the operation of the cooling system 10 in such a way that the cooling system 10 is operated in its stand-by operational state as long as possible.

The stand-by operational state of the cooling system 10 is terminated and normal operation of the cooling system 10 is initiated when cooling energy has to be supplied to cooling energy consumers. To initiate normal operation of the cooling system 10, the first and the second cooling circuit control valves 36, 38 are opened so as to connect the first section 12 a of the cooling circuit 12 to the second section 12 b of the cooling circuit 12 and to provide for a pressure equalization between the first and the second section 12 a, 12 b of the cooling circuit 12. Thereafter, valve 30 is opened such that liquid refrigerant gravity-driven is supplied from the accumulator 28 to the condensers 22 a, 22 b and further to the components of the cooling system 10 arranged downstream of the condensers 22 a, 22 b. Upon flowing through the condensers 22 a, 22 b the refrigerant is super-cooled. Operation of the conveying device 34 is continued.

The supply of refrigerant to the evaporators 14 a, 14 b, 14 c, 14 d is controlled by opening the valves 20 a, 20 b, 20 c, 20 d. When the valves 20 a, 20 b, 20 c, 20 d are open, valve 32 is closed such that refrigerant exiting the condensers 22 a, 22 b is exclusively conveyed to the evaporators 14 a, 14 b, 14 c, 14 d. During further normal operation of the cooling system 10, valve 32 may, however, again be partially closed or entirely closed so as to control the pressure of the refrigerant within the cooling circuit 12 in dependence on the operating state of the evaporators 14 a, 14 b, 14 c, 14 d, i.e. in dependence on the cooling energy demand of the cooling energy consumers supplied with cooling energy by the cooling system 10. Further, the pressure of the refrigerant within the cooling circuit 12 and the supply of refrigerant to the evaporators 14 a, 14 b, 14 c, 14 d is controlled by appropriately controlling the speed of the conveying device 34. Specifically, the operating speed of the conveying device 34 is increased when the cooling requirement of the cooling energy consumers supplied with cooling energy by the evaporators 14 a, 14 b, 14 c, 14 d increases.

During normal operation of the cooling system 10, the second section 12 b of the cooling circuit 12 may be considered as a thermodynamically closed system, wherein the refrigerant is in the state of a wet vapor as soon as the first drop of the refrigerant is condensed. Liquefaction of the refrigerant in this closed system substantially follows the isochores, wherein a pressure drop in the second section 12 b of the cooling circuit 12 is limited by operating the condensers 22 a, 22 b at a low temperature. The evaporators 14 a, 14 b, 14 c, 14 d should be operated at an evaporation temperature of approximately −5° C. The associated pressure in the wet vapor region is approximately 30.5 bar.

During normal operation of the cooling system 10, i.e. when refrigerant is evaporated in the evaporators 14 a, 14 b, 14 c, 14 d so as to supply cooling energy to respective cooling energy consumers, the control unit 52 controls the first cooling circuit control valve 36 such that the pressure in the cooling circuit 12 downstream of the evaporators 14 a, 14 b, 14 c, 14 d and upstream of the condensers 22 a, 22 b is higher than downstream of the condensers 22 a, 22 b and upstream of the evaporators 14 a, 14 b, 14 c, 14 d. Specifically, the first cooling circuit control valve 36 is operated so as to increase or decrease a flow cross-section of the cooling circuit 12 between the evaporators 14 a, 14 b, 14 c, 14 d and the condensers 22 a, 22 b.

The control device 52 during normal operation of the cooling system 10 controls the supply of refrigerant to the evaporators 14 a, 14 b, 14 c, 14 d in dependence on the operational state of the evaporators 14 a, 14 b, 14 c, 14 d, i.e. the cooling energy requirement of the cooling energy consumers coupled to the evaporators 14 a, 14 b, 14 c, 14 d such that a dry evaporation of the refrigerant occurs in the evaporators 14 a, 14 b, 14 c, 14 d. The supply of refrigerant to the individual evaporators 14 a, 14 b, 14 c, 14 d is controlled by suitably controlling the respective valves 20 a, 20 b, 20 c, 20 d.

To shut-down the cooling system 10, the control device 52 controls the operation of the cooling system 10 such that the supply of refrigerant to the evaporators 14 a, 14 b, 14 c, 14 d is interrupted, while liquefaction of refrigerant in the condensers 22 a, 22 b is continued. Liquid refrigerant exiting the condensers 22 a, 22 b is conveyed into the accumulator 28 through open valve 32. During this operational phase of the cooling system 10 the first and the second cooling circuit control valve 36, 38, however, are still open such that the first and the second section 12 a, 12 b of the cooling circuit 12 are still connected to each other. The continued liquefaction of the refrigerant present in the cooling system 10 results in a pressure decrease in the cooling circuit 12, and thus in an evaporation of residual liquid which may be present, in particular, in the first section 12 a of the cooling circuit 12.

Specifically, the control device 52 controls the condensers 22 a, 22 b so as to operate at a low operating temperature, i.e. an operating temperature which is lower than the operating temperature of the condensers 22 a, 22 b during normal operation of the cooling system 10. A low operating temperature of the condenser increases the pressure drop occurring in the cooling system 10 during the shut-down procedure and, as a result, supports the evaporation of residual liquid present in cooling circuit 12.

The control device 52 uses the pressure of the refrigerant in the cooling system 10 or as a control parameter for controlling the operation of the cooling system 10. In particular, the control device 52 continues the shut-down procedure involving an interruption of the supply of refrigerant to the evaporators 14 a, 14 b, 14 c, 14 d and a continued liquefaction of refrigerant in the condensers 22 a, 22 b until a pressure of the refrigerant in the cooling system 12 which may be measured at different locations in the cooling system 12 or at a specific location in the cooling system 12 has reached a predetermined set value. The predetermined set value of the pressure of the refrigerant in the cooling system 12 is lower than a value of the pressure of the refrigerant in the cooling system 12 during normal operation of the cooling system

When the pressure of the refrigerant in the cooling system 12 has reached the predetermine set value, the control device 52 closes the first and the second cooling circuit control valves 36, 38 so as to separate the first section 12 a of the cooling circuit 12 from the second section 12 b of the cooling circuit 12. In this operational state of the cooling system 10, an essential amount of refrigerant present in the cooling system is liquefied, i.e. only a small amount of refrigerant remains in the first section 12 a of the cooling circuit 12. The major part of the refrigerant present in the cooling system 12 is stored in the accumulator 28 which is installed outside of the aircraft cabin 42 in the unpressurized region 40 of the aircraft. The cooling system 10 may be completely shut off by finally ceasing operation of the condensers 22 a, 22 b.

Further, at least one of the valves 20 a, 20 b, 20 c, 20 d may again be opened so as to avoid that the portion of the cooling circuit 12 between the first cooling circuit control valve 36 and the valves 20 a, 20 b, 20 c, 20 d is sealed from the first pressure relief valve 44. By opening at least one of the valves 20 a, 20 b, 20 c, 20 d the portion of the cooling circuit 12 between the first cooling circuit control valve 36 and the valves 20 a, 20 b, 20 c, 20 d may be protected against excess pressure, since refrigerant may be discharged from the portion of the cooling circuit 12 between the first cooling circuit control valve 36 and the valves 20 a, 20 b, 20 c, 20 d via the first pressure relief valve 44.

When a leakage occurs in the cooling system 10 while the system 10 is shut off, the amount of refrigerant which may exit the cooling system 10 and contaminate the ambient air in the aircraft cabin 42 is limited to the small amount of refrigerant prevailing in the first section 12 a of the cooling circuit 12 after system shut-down. In case a leakage occurs in the cooling system 10 during normal system operation, the control device 52 closes the first and the second cooling circuit control valve 36, 38 so as to seal the first and the second section 12 a, 12 b of the cooling system cooling circuit 12 from each other. The amount of refrigerant which may exit the cooling system 10 and contaminate the ambient air in the aircraft cabin 42 then again is limited to the amount of refrigerant present in the first section 12 a of the cooling circuit 12. In addition, the control device 52 opens the bleed valve arrangement 50 so as to discharge refrigerant from the second section 12 b of the cooling circuit 12 into the unpressurized region 40 of the aircraft and to thus minimize the overall amount of refrigerant present in the cooling system 10.

The control unit 52 may control the operation of the first and the second cooling circuit control valve 36, 38 and the bleed valve arrangement 50 in dependence on various sensor signals supplied to the control unit 52. The sensor signals supplied to the control unit 52 may be indicative of a pressure of the refrigerant in the cooling circuit 12 of the cooling system 10, the concentration of the refrigerant in the ambient air in the aircraft cabin 42, an amount of refrigerant present in the cooling circuit 12 of the cooling system 10 and a system failure affecting proper operation of the cooling system. Further, the control unit 52 may close the first and the second cooling circuit control valve 36, 38 and/or open the bleed valve arrangement 50 in dependence on a sensor signal indicative of a predefined operating state of the aircraft, in particular an emergency operating state. For example, the control unit 52 may initiate that the refrigerant is discharged from the cooling system 10 when an emergency landing of the aircraft is intended or in case of a fire on board the aircraft.

In case a leakage occurs in the evaporator 14 d, the refrigerant exiting the evaporator 14 d is received within the encasement 54. This refrigerant may be discharged to the unpressurized region 40 of the aircraft via line 56 by opening valve 58. In particular, the control unit 52 opens valve 58 in dependence on a sensor signal indicative of a pressure in the encasement 54 or a refrigerant concentration in the encasement 54.

The cooling system 10 according to FIG. 2 differs from the arrangement of FIG. 1 in that a storage container 60 a, 60 b is arranged downstream and below each one of the condensers 22 a, 22 b. The storage containers 60 a, 60 b, which may also be formed integral with the condensers 22 a, 22 b are connected to a further accumulator 62 which is arranged downstream and below the storage containers 60 a, 60 b. Liquid refrigerant may be conveyed gravity-driven from the accumulator 28 and the storage containers 60 a, 60 b into the further accumulator 62. Valve 30 present in the arrangement of FIG. 1 is dispensed with. The storage containers 60 a, 60 b and the accumulators 28, 62 are dimensioned so as to be able to receive the entire amount of refrigerant present in the cooling system 10 in its liquid state of aggregation. Thus, during system start-up and during stand-by operation of the cooling system, the condensers 22 a, 22 b may be operated so as to liquefy refrigerant without it being necessary to operate the conveying device 34.

The cooling system 10 further comprises two super-coolers 64 a, 64 b which are arranged in series in the cooling circuit 12 downstream of the further accumulator 62. The conveying device 34 is installed above the storage containers 60 a, 60 b and the further accumulator 62 and therefore is designed in the form of a self-sucking pump. Further, the conveying device 34 no longer is disposed upstream, but instead downstream of the second cooling circuit control valve 38. In other words, the conveying device 34 no longer is disposed in the second section 12 b of cooling circuit 12, but in the first section 12 a of the cooling circuit 12. Therefore the conveying device 34 is less susceptible to leakages and also may be designed so as to be less pressure resistant than in the arrangement of FIG. 1. Finally, valve 32 is designed in the form of a mechanically actuated pressure relief valve.

Otherwise, the structure and the operating principle of the cooling system 10 according to FIG. 2 correspond to the structure and the operating principle of the arrangement of FIG. 1.

The cooling system 10 according to FIG. 3 differs from the arrangement of FIG. 2 in that the conveying device 34, like in the arrangement according to FIG. 1, again is disposed upstream of the second cooling circuit control valve 38 and thus arranged in the second section 12 b of cooling circuit 12. Further, each one of the first and the second cooling circuit control valve 36, 38 is associated with an additional pipe burst safety valve 66 a, 66 b. The pipe burst safety valve 66 a associated with the first cooling circuit control valve 36 is arranged upstream of the first cooling circuit control valve 36. The pipe burst safety valve 66 b associated with the second cooling circuit control valve 38 is arranged downstream of the second cooling circuit control valve 38. In case a pipe bust should occur in the tubing of the cooling circuit 12, in particular in the tubing of the first section 12 a of the cooling circuit 12, the pipe burst safety valves 66 a, 66 b immediately close such that the amount of refrigerant exiting the cooling system 10 due to the pipe burst is limited.

The cooling system 10 of FIG. 3 further comprises an additional pressure relief valve 68 disposed in the cooling circuit 12 between the evaporators 14 a, 14 b, 14 c, 14 d and the first cooling circuit control valve 36. Like the pressure relief valves 44, 46, the additional pressure relief valve 68 is designed as mechanically actuatable valve which automatically opens in case a pressure difference acting on the valve 68 exceeds a threshold value which is determined by the design of the valve 68. Due to the presence of the additional pressure relief valve 68 it is no longer necessary to maintain at least one of the valves 20 a, 20 b, 20 c, 20 d open when the system 10 is shut off so as to prevent built-up of an excess pressure in the portion of the cooling circuit 12 between the evaporators 14 a, 14 b, 14 c, 14 d and the first cooling circuit control valve 36.

Finally, the cooling system 10 of FIG. 3 comprises a bleed valve arrangement 70 which in its open state serves to discharge refrigerant from the first section 12 a of the cooling circuit 12 to the unpressurized region 40 of the aircraft. The bleed valve arrangement 70 is formed by an electrically actuatable safety valve which is connected to the first section 12 a of the cooling circuit 12 via a connecting line 72. The bleed valve arrangement 70 may be controlled by the control unit 52 as described above in connection with the bleed valve arrangement 50. The additional pressure relief valve 68 and the bleed valve arrangement 70 are connected to a gas line of the cooling circuit 12 extending downstream of the evaporators 14 a, 14 b, 14 c, 14 d and thus having a larger flow cross section than a liquid line of the cooling circuit 12 extending upstream of the evaporators 14 a, 14 b, 14 c, 14 d. As a result, a large amount of refrigerant can be quickly discharged from the cooling system 10 via the additional pressure relief valve 68 and the bleed valve arrangement 70.

Otherwise, the structure and the operating principle of the cooling system 10 according to FIG. 3 correspond to the structure and the operating principle of the arrangement of FIG. 2.

The cooling system 10 according to FIG. 4 differs from the arrangement of FIG. 3 in that the cooling circuit 12 of the cooling system 10 comprises two first sections 12 a, 12 a′ which are formed separate from each other. Two evaporators 14 a, 14 b are disposed in the first cooling circuit section 12 a, and two evaporators 14 c, 14 d are disposed in the first cooling circuit section 12 a′. A first and a second cooling circuit control valve 36, 38 in their closed state serve to seal the first cooling circuit section 12 a from the second cooling circuit section 12 b. A first and a second cooling circuit control valve 36′, 38′ in their closed state serve to seal the first cooling circuit section 12 a′ from the second cooling circuit section 12 b. Pipe burst safety valves 66 a, 66 a′, 66 b, 66 b′ are associated with each of the first and the second cooling circuit control valves 36, 36′, 38, 38′. The pipe burst safety valves 66 a, 66 a′, 66 b, 66 b′ may be disposed in the cooling circuit 12 at the positions shown in FIG. 4. It is, however, advantageous to install the pipe burst safety valves 66 a, 66 a′, 66 b, 66 b′ in the unpressurized aircraft region 40 so as to allow refrigerant discharged from the cooling system via the pipe burst safety valves 66 a, 66 a′, 66 b, 66 b′ to be vented to the unpressurized aircraft region 40 and finally the aircraft environment.

The cooling system 10 further comprises two first pressure relief valves 44, 44′ wherein the first pressure relief valves 44 is associated with the first cooling circuit section 12 a, and wherein the first pressure relief valves 44′ is associated with the first cooling circuit section 12 a′. In addition an additional pressure relief valve 68 is associated with the first cooling circuit section 12 a, whereas an additional pressure relief valve 68′ is associated with the first cooling circuit section 12 a′. Finally two bleed valve arrangements 70, 70′ are present, wherein the bleed valve arrangement 70 is associated with the first cooling circuit section 12 a, whereas the bleed valve arrangement 70′ is associated with the first cooling circuit section 12 a′.

The evaporators 14 a, 14 b, 14 c, 14 d disposed in the two first cooling circuit sections 12 a, 12 a′ may be operated independently from each other, i.e. it is possible to operate an evaporator 14 a, 14 b, 14 c, 14 d disposed in one first cooling circuit section 12 a, 12 a′, but not to operate an evaporator 14 a, 14 b, 14 c, 14 d disposed in the other first cooling circuit section 12 a, 12 a′. Further, by suitable controlling the cooling circuit control valves 36, 36′, 38, 38′, the two first cooling circuit sections 12 a, 12 a′ may be sealed from the second cooling circuit section 12 b independently from each other.

Otherwise, the structure and the operating principle of the cooling system 10 according to FIG. 4 correspond to the structure and the operating principle of the arrangement of FIG. 3.

The cooling system 10 according to FIG. 5 differs from the arrangement of FIG. 4 in that an additional line is provided for connecting an outlet of the conveying device 34 to the accumulator 28. An additional valve 32′ is provided to control the supply of refrigerant from the conveying device 34 to the accumulator 28. This arrangement increases redundancy in case of a failure of one of the valves 32, 32′. Further, also for increasing system redundancy, beside the cooling circuit control valves 36, 36′, 38, 38′, additional cooling circuit control valves 74, 76 are provided which, in their closed state, allow to seal both first cooling circuit sections 12 a, 12 a′ from the second cooling circuit section 12 b.

Moreover, additional bleed valve arrangements 78, 78′ further improve the operational safety of the cooling system 10, wherein the bleed valve arrangement 78 is associated with the first cooling circuit section 12 a, whereas the bleed valve arrangement 78′ is associated with the first cooling circuit section 12 a′. Further additional pressure relief valves 80, 80′ also improve the operational safety of the cooling system 10. Since the evaporators 14 a, 14 b, 14 c, 14 d may be susceptible to pipe burst, each one of the evaporators 14 a, 14 b, 14 c, 14 d is disposed between a respective pair of additional pipe burst valves 82, 82′. Bypass lines 84, 86, 84′, 86′ are provided for bypassing the evaporators 14 a, 14 b and the evaporators 14 c, 14 d, respectively, wherein the refrigerant flow through bypass lines 84, 84′ is controlled by respective pressure relief valves 88, 88′, whereas the refrigerant flow through bypass lines 86, 86′ is controlled by respective control valves 90, 90′.

Otherwise, the structure and the operating principle of the cooling system 10 according to FIG. 5 correspond to the structure and the operating principle of the arrangement of FIG. 4.

As an alternative to the cooling circuit control valve arrangement shown in FIG. 5, an arrangement according to FIG. 6 can be employed in the cooling system of FIG. 5. The modular arrangement according to FIG. 6 comprises two cooling circuit control valves, for example cooling circuit control valves 74 and 36, which are connected in series with a volume 92. Additional pressure relief valves 94, 96 may be employed in the modular arrangement according to FIG. 6.

The features of the different cooling system embodiments described above with reference to FIGS. 1 to 6 may be combined in an arbitrary manner. Further, selected features of the exemplary embodiments described herein may be dispensed with. For example, the cooling system of FIG. 5 does not necessarily have to comprise all the features depicted in FIG. 5. Instead, selected components such as for example lines, valves and the like may be dispensed with as desired.

In the embodiments of a cooling system 10 described above, the accumulator 28 fulfills the double function of storing liquid refrigerant exiting the condensers 22 a, 22 b and, in addition thereto, of reducing the system pressure in the cooling circuit 12. The pressure reducing effect of the accumulator 28 results from the additional volume the accumulator 28 adds to the volume of the cooling circuit 12 and becomes more and more significant, as the volume of the accumulator 28 increases. The importance of the pressure reduction function of the accumulator 28 increases as the operating temperature of the cooling system 10 and hence the pressure in the cooling circuit 12 increases and is of particular relevance if the cooling system 10 is operated with a refrigerant causing a high system pressure such as, for example, CO₂.

Basically the cooling system 10 may comprise only the accumulator 28 as described above, which may serve to store liquid refrigerant exiting the condensers 22 a, 22 b and to reduce the system pressure in the cooling circuit 12. Alternatively, the accumulator 28 may be dispensed with, but the cooling system 10 may be equipped with a storage container. In such a cooling system 10 the storage container may fulfill the double function of storing liquid refrigerant exiting the condensers 22 a, 22 b and of reducing the system pressure in the cooling circuit 12. It is, however, also conceivable to equip the cooling system 10 with the accumulator 28 and an additional storage container, wherein either both components or only one of the accumulator 28 and the storage container may serve to store liquid refrigerant exiting the condensers 22 a, 22 b and to reduce the system pressure in the cooling circuit 12. Finally, a configuration of the cooling system 10 is conceivable, wherein the accumulator 28 serves to collect and to store liquid refrigerant, whereas the storage container, due to its additional volume, serves to reduce the system pressure.

In case the functions “storing liquid refrigerant” and “reducing system pressure” in the cooling system 10 are provided by two separate components, these components may be installed at different positions within the cooling circuit 12, allowing to more efficiently use the available installation space and to limit the size of the individual components of the cooling system 10. However, the pressure reducing storage container then preferably is installed in a high pressure portion of the cooling circuit 12 in order to reliably prevent the pressure in the high pressure portion of the cooling circuit 12 from exceeding a predetermined maximum value.

Further, in case the storage container merely serves to control the pressure in the cooling system 10, it is not necessary to provide for a direct fluid connection between the accumulator 28 and the storage container. Instead, the storage container may be connected to the cooling circuit 12 via only a single line branching off from the cooling circuit 12, for example, upstream of the condensers 22 a, 22 b and downstream of the evaporators 14 a, 14 b, 14 c, 14 d. The line connecting the storage container to the cooling circuit 12 preferably is connected to the storage container at the geodetic lowest point of storage container. This configuration ensures that the storage container is supplied only with gaseous refrigerant which is discharged from the cooling circuit 12 due to the pressure in the cooling circuit 12 exceeding a predetermined value. Of course, if desired, two storage containers may be provided, in the cooling system 10, wherein a first storage container may be connected to the cooling circuit 12 via a line branching off from the cooling circuit 12 upstream of the first condenser 22 a and downstream of the evaporators 14 a, 14 b, 14 c, 14 d and wherein a second storage container may be connected to the cooling circuit 12 via a line branching off from the cooling circuit 12 upstream of the second condenser 22 b and downstream of the evaporators 14 a, 14 b, 14 c, 14 d. 

1. Aircraft comprising a cooling system, wherein the cooling system comprises: a cooling circuit allowing circulation of a two-phase refrigerant therethrough, an evaporator disposed in a first section of the cooling circuit and having a refrigerant inlet and a refrigerant outlet, a condenser disposed in a second section of the cooling circuit and having a refrigerant inlet and a refrigerant outlet, a first cooling circuit control valve disposed in the cooling circuit between the refrigerant outlet of the evaporator and the refrigerant inlet of the condenser, and a second cooling circuit control valve disposed in the cooling circuit between the refrigerant outlet of the condenser and the refrigerant inlet of the evaporator, the first and the second cooling circuit control valve in their closed state being adapted to seal the first section of the cooling circuit from the second section of the cooling circuit, wherein the second section of the cooling circuit is installed in an unpressurized region of the aircraft.
 2. Aircraft according to claim 1, wherein the cooling system further comprises at least one of: a first bleed valve arrangement which in its open state is adapted to discharge refrigerant from the first section of the cooling circuit to at least one of the aircraft environment and an unpressurized region of the aircraft, and a second bleed valve arrangement which in its open state is adapted to discharge refrigerant from the second section of the cooling circuit to at least one of the aircraft environment and an unpressurized region of the aircraft.
 3. Aircraft according to claim 1, wherein a control device of the cooling system is configured to control at least one of the first and the second cooling circuit control valve, the first bleed valve arrangement and the second bleed valve arrangement in dependence on at least one sensor signal supplied to the control device, the sensor signal being indicative of at least one of a pressure of the refrigerant in the cooling circuit of the cooling system, a concentration of the refrigerant in the ambient air in a pressurized region of the aircraft, an amount of refrigerant present in the cooling circuit of the cooling system, a system failure affecting proper operation of the cooling system, and a predefined operating state of the aircraft.
 4. Aircraft according to claim 1, wherein at least one component of the cooling system which is installed in a pressurized region of the aircraft comprises an encasement, the encasement being adapted to receive refrigerant leaking from the least one component of the cooling system.
 5. Aircraft according to claim 1, wherein a control device of the cooling system is configured to control the operation of the cooling system upon system start-up such that refrigerant is liquefied in the condenser while the first cooling circuit control valve and the second cooling circuit control valve are closed so as to separate the first section of the cooling circuit from the second section of the cooling circuit until the amount of liquid refrigerant is sufficient to allow a flooding of cooling system components which are disposed in the cooling circuit downstream of a conveying device for conveying refrigerant through the cooling circuit with liquid refrigerant.
 6. Aircraft according to claim 1, wherein a control device of the cooling system is configured to control the supply of refrigerant to the evaporator in dependence on the operational state of the evaporator such that a dry evaporation of the refrigerant occurs in the evaporator.
 7. Aircraft according to claim 1, wherein a control device of the cooling system is configured to control the operation of the cooling system upon system shut-down such that the supply of refrigerant to the evaporator is interrupted while liquefaction of refrigerant in the condenser is continued until a pressure of the refrigerant in the cooling system has reached a predetermined set value.
 8. Aircraft according to claim 7, wherein the predetermined set value of the pressure of the refrigerant in the cooling system is lower than a value of the pressure of the refrigerant in the cooling system during normal operation of the cooling system.
 9. Aircraft according to claim 7, wherein a control device of the cooling system is configured to close the first and the second cooling circuit control valve so as to separate the first section of the cooling circuit from the second section of the cooling circuit when the pressure of the refrigerant in the cooling system has reached the predetermined set value.
 10. Aircraft according to claims 1, wherein a control device of the cooling system is configured to control the operation of the cooling system upon system shut-down such that refrigerant which is liquefied in the condenser is stored in an accumulator which is installed in an unpressurized region of the aircraft.
 11. Aircraft according to claim 1, wherein a pipe burst safety valve is associated with each one of the first and the second cooling circuit control valve.
 12. Aircraft according to claim 1, wherein the cooling circuit comprises two first sections which are at least partially installed in a pressurized region of the aircraft, wherein an evaporator is disposed in each of the two first sections, and wherein two first cooling circuit control valves as well as two second cooling circuit control valves in their closed state are adapted to seal the two first sections of the cooling circuit from the second section of the cooling circuit.
 13. Aircraft according to claim 12, wherein a control device of the cooling system is configured to control at least one of the two first cooling circuit control valves and the two second cooling circuit control valves in such a manner that only one of the two first sections of the cooling circuit is connected to the second section of the cooling circuit if the amount of refrigerant circulating in the cooling circuit is not sufficient to satisfy the demand of both first cooling circuit sections.
 14. Aircraft according to claim 1, wherein the cooling system further comprises a first additional cooling circuit control valve connected in series with at least one of the first cooling circuit control valve and a second additional cooling circuit control valve connected in series with the second cooling circuit control valve, and/or wherein at least one cooling system component which is susceptible to pipe burst is disposed between a respective pair of additional pipe burst valves.
 15. Aircraft according to claim 1, wherein the cooling system further comprises a bypass line bypassing the evaporator, wherein at least one of a pressure relief valve and a control valve may be adapted to control the refrigerant flow through the bypass line. 